The Del Air Rockhounds Club, Inc
Los Angeles - San Fernando Valley, California, United States
- We are a non-profit organization dedicated to sharing knowledge of the lapidary arts and techniques, geology, mineralogy and related fields.

You found fossil
whale bone on our January field trip, but what kind of whale bone are you
really holding in your hand? Club member Keri Dearborn is a naturalist and
environmental educator. She has taught marine mammal zoology and participated
in local marine mammal research. We'll look at our local fossilized whale bone
with an emphasis on its geological and historical significance and we'll
connect it to modern whale populations. Are whales more closely related to
wolves or deer? Is your whale bone fossil from a predator or prey animal? What
makes whale bone easily identifiable from other mammals? California's coast has
been populated by whales for millions of years and continues to be home to one
of the world's most robust whale and dolphin populations. How is your piece of
fossil whale bone a link to the past and the future? Emmy Silverman, Program Director

Go
to www.cfmsinc.org for more show
information.************************************************************February
2016 “Something of the Month”

"Thundereggs"

A thunderegg is a nodule-like
rock, similar to a filled geode. Thundereggs are rough spheres, most about the
size of a baseball though they can range from less than an inch to over a meter
across. They usually contain centres of chalcedony, agate, jasper or opal either
uniquely or in combination. Also frequently encountered are quartz and gypsum
crystals, as well as various other mineral growths and inclusions.

Thundereggs usually look
like ordinary rocks on the outside, but slicing them in half and polishing them
may reveal intricate patterns and colors.Thunderegg is not synonymous with
either geode or agate. A geode is a simple term for a rock with a hollow in it,
often with crystal formation. A thunderegg on the other hand is a specific
geological structure. A thunderegg may be referred to as a geode if it has a
hollow in it, but not all geodes are thundereggs because there are many
different ways for a hollow to form.

Thundereggs are
found in flows of rhyolite lava. They form in gas pockets in the lava, which
act as molds, from the action of water percolating through the porous rock
carrying silica in solution. The deposits lined and filled the cavity, first
with a darker matrix material, then an inner core of agate or chalcedony. The
various colors come from differences in the minerals found in the soil and rock
that the water has moved through.

On March 30, 1965, the thunderegg was designated as the Oregon state rock.
While thundereggs can be collected all over Oregon, the largest deposits are
found in Crook, Jefferson, Malheur, Wasco and Wheeler counties. The world’s
largest thunderegg, a 1.75 ton specimen, is housed by the Rice Northwest Museum
of Rocks and Minerals in Oregon.*************************************************************

It was an absolutely beautiful day at Refugio
State Beach. We could not have asked for better weather. There were perhaps 20
surfers and 8 rockhounds at the beach that day. The 8 rockhounds were club
members Jeff Dengrove, Chris Ward, Bob Knox, Richard, Emily & Nicolas
Haering and guests Iris Delarosa and her friend Marilyn. We all arrived right
around noon and immediately went on the hunt. Not only was there a multitude of
whale bone to be found but also many marine fossils, agate, petrified palm
root, jasper and sea sponge. All eight of us brought lunches and drinks and
enjoyed a mid-afternoon picnic on the beach. After lunch it was back to the
hunt. Jeff Dengrove drove down the road to check out Gaviota but returned
advising the rest of us the beach over there was covered in sand. All 8 of us
stayed at Refugio the entire time and did not leave till the sun went down….and
all went home will multiple bags of beach found treasures. I think this was the
best hunt in the 10 years I have been attending this event.**********************************************